The present invention relates to methods of inhibiting corrosion of metal surfaces in contact with an aqueous medium of corrosive nature. More particularly, this invention relates to methods of inhibiting the corrosion of metal surfaces by utilizing in the corrosive aqueous medium certain phosphonomethyl amino carboxylates either alone or in combination with one or more other corrosion inhibitor compounds.
The present invention has special utility in the prevention of the corrosion of metals which are in contact with circulating water, that is water which is moving through condensers, engine jackets, cooling towers, evaporators or distribution sytems; however, it can be used to prevent the corrosion of metal surfaces in other aqueous corrosive media. This invention is especially valuable in inhibiting the corrosion of ferrous metals including iron and steel, and also galvanized steel, nonferrous metals including copper and its alloys, aluminum and its alloys and brass. These metals are generally used in circulating water systems.
The major corrosive ingredients of aqueous cooling systems are primarily dissolved oxygen and inorganic salts, such as the carbonate, bicarbonate, chloride and/or sulfate salts of calcium, magnesium and/or sodium. Other factors contributing to corrosion are pH and temperature. Generally an increase in the temperature and a decrease in the pH accelerates corrosion.
It is well-known that certain corrosion inhibiting compositions of organic phosphonates are enhanced in their effectiveness by the addition of zinc salts and/or chromates to the inhibiting composition. However, the use of zinc salts and chromates has been found in recent years to adversely affect water quality when released in natural waters. Removal of the zinc and/or chromate ions by precipitation or other treatments is complicated and expensive. Consequently, effective corrosion inhibiting compositions free of such heavy metal ions are now desired by industry for protection of metallic equipment without the accompanying disadvantages of the heavy metal ions previously employed.